FWIW a long time ago I wanted fast XORing of 512-byte “sectors” of Rar files. Initially I think I used array.array with the largest word size available, or numpy if available. Later when I learnt more Python I discovered the int.from_bytes() trick, and used int(hexlify(...), 16) in Python 2. So I guess the array module was a relatively obvious place to look, and the long integer trick was unexpected (I’d never programmed with unlimited size integers before).

Serhiy’s bit array idea also seems interesting. I bet somebody has already written a package. Maybe it could also be useful for things like Huffman encoding, where you string various bit strings together into a sequence of bytes. But I do wonder if all these things are too specialized for Python’s standard library.